The broad objective is a continuation study of the effect of 5- iodo-2'- deoxyuridine, IdUrd, and related analogs on the replication of neoplastic cells and viruses. Studies on the augmentation of radiation sensitization by such compounds will be investigated on the enzyme level, in cell culture and eventually in vivo. Potential anti- neoplastic as well as antiviral agents will be prepared, however, the major thrust is our study of the potentiation of the sensitization of neoplastic tissues to the lethal effects of radiation. Elucidation of the biochemical consequences of incorporation of IdUrd into DNA is also under investiation.